The search for sustainable energy sources has prompted many studies into wave generation. One device commonly used in wave generation systems is an Oscillating Water Column (OWC). This is a hollow vessel, with one open end. When partially submerged in waves, with the open end in the water, the OWC contains a column of water and a region of air trapped at the top. The water level within the OWC alternately rises and falls with the waves. This acts as a piston and creates a corresponding pattern of alternating positive and negative pressure at the top of the OWC.
This comprises a partly submerged structure which is open to the sea below the water surface so that it contains a column of water. Air is trapped above the surface of the water column. As waves enter and exit the collector, the water column moves up and down and acts like a piston on the air, pushing it back and forth.
GB 2 069 061 is an example of an existing system in which air flows from an OWC through a valve into a resilient chamber having elastic characteristics, through another valve into a turbine, then into an exhaust chamber, through a third valve and back into the OWC. This invention requires that the resilient chamber be surrounded by the exhaust chamber.
In CA 2 286 545, when there is positive pressure in the OWC, air passes through a valve into an annular chamber and over turbines 54. The air is then discharged to the atmosphere through an exit port. When the water level falls, the air flow is reversed and air is drawn from the atmosphere over the turbines and back into the OWC. This system therefore requires the use of specialised dual-directional turbines in order to extract energy.
In SU 1097819 the motion of the waves drives a hydraulic pump to force water into a pneumohydraulic accumulator. It is the water which does the work in this system, rather than the air from an OWC.
Many wave generation systems are designed to operate on deep-sea ocean waves because of the massive amounts of energy available at a given point. This creates two major problems. The first is that the amount of energy is unpredictable and can vary from negligible amounts to storm related destructive forces. The second is that often the large distance from shore requires costly cabling systems and suffers from the inevitable losses involved in transmission.
Near-shore waves, although smaller, are much more reliable and consistent than ocean swells. A near-shore energy collection system reduces energy loss, eliminates the need for expensive cabling and improves accessibility for maintenance or construction.
However, near-shore conditions and topology vary greatly along different coastlines, requiring custom made systems to fit local requirements.